1 //===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the default implementation of the Alias Analysis interface
11 // that simply implements a few identities (two different globals cannot alias,
12 // etc), but otherwise does no analysis.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Analysis/AliasAnalysis.h"
17 #include "llvm/Analysis/Passes.h"
18 #include "llvm/Constants.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Function.h"
21 #include "llvm/ParameterAttributes.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/Intrinsics.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/STLExtras.h"
29 #include "llvm/Support/Compiler.h"
30 #include "llvm/Support/GetElementPtrTypeIterator.h"
31 #include "llvm/Support/ManagedStatic.h"
36 /// NoAA - This class implements the -no-aa pass, which always returns "I
37 /// don't know" for alias queries. NoAA is unlike other alias analysis
38 /// implementations, in that it does not chain to a previous analysis. As
39 /// such it doesn't follow many of the rules that other alias analyses must.
41 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
42 static char ID; // Class identification, replacement for typeinfo
43 NoAA() : ImmutablePass((intptr_t)&ID) {}
44 explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
46 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
47 AU.addRequired<TargetData>();
50 virtual void initializePass() {
51 TD = &getAnalysis<TargetData>();
54 virtual AliasResult alias(const Value *V1, unsigned V1Size,
55 const Value *V2, unsigned V2Size) {
59 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
60 std::vector<PointerAccessInfo> *Info) {
61 return UnknownModRefBehavior;
64 virtual void getArgumentAccesses(Function *F, CallSite CS,
65 std::vector<PointerAccessInfo> &Info) {
66 assert(0 && "This method may not be called on this function!");
69 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
70 virtual bool pointsToConstantMemory(const Value *P) { return false; }
71 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
74 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
77 virtual bool hasNoModRefInfoForCalls() const { return true; }
79 virtual void deleteValue(Value *V) {}
80 virtual void copyValue(Value *From, Value *To) {}
83 // Register this pass...
86 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
88 // Declare that we implement the AliasAnalysis interface
89 RegisterAnalysisGroup<AliasAnalysis> V(U);
90 } // End of anonymous namespace
92 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
95 /// BasicAliasAnalysis - This is the default alias analysis implementation.
96 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
97 /// derives from the NoAA class.
98 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
99 static char ID; // Class identification, replacement for typeinfo
100 BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
101 AliasResult alias(const Value *V1, unsigned V1Size,
102 const Value *V2, unsigned V2Size);
104 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
105 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
106 return NoAA::getModRefInfo(CS1,CS2);
109 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
110 /// non-escaping allocations.
111 virtual bool hasNoModRefInfoForCalls() const { return false; }
113 /// pointsToConstantMemory - Chase pointers until we find a (constant
115 bool pointsToConstantMemory(const Value *P);
118 // CheckGEPInstructions - Check two GEP instructions with known
119 // must-aliasing base pointers. This checks to see if the index expressions
120 // preclude the pointers from aliasing...
122 CheckGEPInstructions(const Type* BasePtr1Ty,
123 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
124 const Type *BasePtr2Ty,
125 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
128 // Register this pass...
129 char BasicAliasAnalysis::ID = 0;
130 RegisterPass<BasicAliasAnalysis>
131 X("basicaa", "Basic Alias Analysis (default AA impl)");
133 // Declare that we implement the AliasAnalysis interface
134 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
135 } // End of anonymous namespace
137 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
138 return new BasicAliasAnalysis();
141 // getUnderlyingObject - This traverses the use chain to figure out what object
142 // the specified value points to. If the value points to, or is derived from, a
143 // unique object or an argument, return it.
144 static const Value *getUnderlyingObject(const Value *V) {
145 if (!isa<PointerType>(V->getType())) return 0;
147 // If we are at some type of object, return it. GlobalValues and Allocations
148 // have unique addresses.
149 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
152 // Traverse through different addressing mechanisms...
153 if (const Instruction *I = dyn_cast<Instruction>(V)) {
154 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
155 return getUnderlyingObject(I->getOperand(0));
156 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
157 if (CE->getOpcode() == Instruction::BitCast ||
158 CE->getOpcode() == Instruction::GetElementPtr)
159 return getUnderlyingObject(CE->getOperand(0));
164 static const User *isGEP(const Value *V) {
165 if (isa<GetElementPtrInst>(V) ||
166 (isa<ConstantExpr>(V) &&
167 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
168 return cast<User>(V);
172 static const Value *GetGEPOperands(const Value *V,
173 SmallVector<Value*, 16> &GEPOps){
174 assert(GEPOps.empty() && "Expect empty list to populate!");
175 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
176 cast<User>(V)->op_end());
178 // Accumulate all of the chained indexes into the operand array
179 V = cast<User>(V)->getOperand(0);
181 while (const User *G = isGEP(V)) {
182 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
183 !cast<Constant>(GEPOps[0])->isNullValue())
184 break; // Don't handle folding arbitrary pointer offsets yet...
185 GEPOps.erase(GEPOps.begin()); // Drop the zero index
186 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
187 V = G->getOperand(0);
192 /// pointsToConstantMemory - Chase pointers until we find a (constant
194 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
195 if (const Value *V = getUnderlyingObject(P))
196 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
197 return GV->isConstant();
201 // Determine if an AllocationInst instruction escapes from the function it is
202 // contained in. If it does not escape, there is no way for another function to
203 // mod/ref it. We do this by looking at its uses and determining if the uses
204 // can escape (recursively).
205 static bool AddressMightEscape(const Value *V) {
206 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
208 const Instruction *I = cast<Instruction>(*UI);
209 switch (I->getOpcode()) {
210 case Instruction::Load:
212 case Instruction::Store:
213 if (I->getOperand(0) == V)
214 return true; // Escapes if the pointer is stored.
216 case Instruction::GetElementPtr:
217 if (AddressMightEscape(I))
220 case Instruction::BitCast:
221 if (!isa<PointerType>(I->getType()))
223 if (AddressMightEscape(I))
226 case Instruction::Ret:
227 // If returned, the address will escape to calling functions, but no
228 // callees could modify it.
237 // getModRefInfo - Check to see if the specified callsite can clobber the
238 // specified memory object. Since we only look at local properties of this
239 // function, we really can't say much about this query. We do, however, use
240 // simple "address taken" analysis on local objects.
242 AliasAnalysis::ModRefResult
243 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
244 if (!isa<Constant>(P))
245 if (const AllocationInst *AI =
246 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
247 // Okay, the pointer is to a stack allocated object. If we can prove that
248 // the pointer never "escapes", then we know the call cannot clobber it,
249 // because it simply can't get its address.
250 if (!AddressMightEscape(AI))
253 // If this is a tail call and P points to a stack location, we know that
254 // the tail call cannot access or modify the local stack.
255 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
256 if (CI->isTailCall() && isa<AllocaInst>(AI))
260 // The AliasAnalysis base class has some smarts, lets use them.
261 return AliasAnalysis::getModRefInfo(CS, P, Size);
264 static bool isNoAliasArgument(const Argument *Arg) {
265 const Function *Func = Arg->getParent();
266 const ParamAttrsList *Attr = Func->getParamAttrs();
269 for (Function::const_arg_iterator I = Func->arg_begin(),
270 E = Func->arg_end(); I != E; ++I, ++Idx) {
272 Attr->paramHasAttr(Idx, ParamAttr::NoAlias))
279 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
280 // as array references. Note that this function is heavily tail recursive.
281 // Hopefully we have a smart C++ compiler. :)
283 AliasAnalysis::AliasResult
284 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
285 const Value *V2, unsigned V2Size) {
286 // Strip off any constant expression casts if they exist
287 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
288 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
289 V1 = CE->getOperand(0);
290 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
291 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
292 V2 = CE->getOperand(0);
294 // Are we checking for alias of the same value?
295 if (V1 == V2) return MustAlias;
297 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
298 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
299 return NoAlias; // Scalars cannot alias each other
301 // Strip off cast instructions...
302 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
303 return alias(I->getOperand(0), V1Size, V2, V2Size);
304 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
305 return alias(V1, V1Size, I->getOperand(0), V2Size);
307 // Figure out what objects these things are pointing to if we can...
308 const Value *O1 = getUnderlyingObject(V1);
309 const Value *O2 = getUnderlyingObject(V2);
311 // Pointing at a discernible object?
314 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
315 // Incoming argument cannot alias locally allocated object!
316 if (isa<AllocationInst>(O2)) return NoAlias;
318 // If they are two different objects, and one is a noalias argument
319 // then they do not alias.
320 if (O1 != O2 && isNoAliasArgument(O1Arg))
323 // Otherwise, nothing is known...
326 if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
327 // Incoming argument cannot alias locally allocated object!
328 if (isa<AllocationInst>(O1)) return NoAlias;
330 // If they are two different objects, and one is a noalias argument
331 // then they do not alias.
332 if (O1 != O2 && isNoAliasArgument(O2Arg))
335 // Otherwise, nothing is known...
337 } else if (O1 != O2) {
338 if (!isa<Argument>(O1))
339 // If they are two different objects, and neither is an argument,
340 // we know that we have no alias...
344 // If they are the same object, they we can look at the indexes. If they
345 // index off of the object is the same for both pointers, they must alias.
346 // If they are provably different, they must not alias. Otherwise, we
347 // can't tell anything.
351 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
352 return NoAlias; // Unique values don't alias null
354 if (isa<GlobalVariable>(O1) ||
355 (isa<AllocationInst>(O1) &&
356 !cast<AllocationInst>(O1)->isArrayAllocation()))
357 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
358 // If the size of the other access is larger than the total size of the
359 // global/alloca/malloc, it cannot be accessing the global (it's
360 // undefined to load or store bytes before or after an object).
361 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
362 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
363 if (GlobalSize < V2Size && V2Size != ~0U)
369 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
370 return NoAlias; // Unique values don't alias null
372 if (isa<GlobalVariable>(O2) ||
373 (isa<AllocationInst>(O2) &&
374 !cast<AllocationInst>(O2)->isArrayAllocation()))
375 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
376 // If the size of the other access is larger than the total size of the
377 // global/alloca/malloc, it cannot be accessing the object (it's
378 // undefined to load or store bytes before or after an object).
379 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
380 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
381 if (GlobalSize < V1Size && V1Size != ~0U)
386 // If we have two gep instructions with must-alias'ing base pointers, figure
387 // out if the indexes to the GEP tell us anything about the derived pointer.
388 // Note that we also handle chains of getelementptr instructions as well as
389 // constant expression getelementptrs here.
391 if (isGEP(V1) && isGEP(V2)) {
392 // Drill down into the first non-gep value, to test for must-aliasing of
393 // the base pointers.
394 const Value *BasePtr1 = V1, *BasePtr2 = V2;
396 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
397 } while (isGEP(BasePtr1) &&
398 cast<User>(BasePtr1)->getOperand(1) ==
399 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
401 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
402 } while (isGEP(BasePtr2) &&
403 cast<User>(BasePtr2)->getOperand(1) ==
404 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
406 // Do the base pointers alias?
407 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
408 if (BaseAlias == NoAlias) return NoAlias;
409 if (BaseAlias == MustAlias) {
410 // If the base pointers alias each other exactly, check to see if we can
411 // figure out anything about the resultant pointers, to try to prove
414 // Collect all of the chained GEP operands together into one simple place
415 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
416 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
417 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
419 // If GetGEPOperands were able to fold to the same must-aliased pointer,
420 // do the comparison.
421 if (BasePtr1 == BasePtr2) {
423 CheckGEPInstructions(BasePtr1->getType(),
424 &GEP1Ops[0], GEP1Ops.size(), V1Size,
426 &GEP2Ops[0], GEP2Ops.size(), V2Size);
427 if (GAlias != MayAlias)
433 // Check to see if these two pointers are related by a getelementptr
434 // instruction. If one pointer is a GEP with a non-zero index of the other
435 // pointer, we know they cannot alias.
439 std::swap(V1Size, V2Size);
442 if (V1Size != ~0U && V2Size != ~0U)
444 SmallVector<Value*, 16> GEPOperands;
445 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
447 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
448 if (R == MustAlias) {
449 // If there is at least one non-zero constant index, we know they cannot
451 bool ConstantFound = false;
452 bool AllZerosFound = true;
453 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
454 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
455 if (!C->isNullValue()) {
456 ConstantFound = true;
457 AllZerosFound = false;
461 AllZerosFound = false;
464 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
465 // the ptr, the end result is a must alias also.
470 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
473 // Otherwise we have to check to see that the distance is more than
474 // the size of the argument... build an index vector that is equal to
475 // the arguments provided, except substitute 0's for any variable
476 // indexes we find...
477 if (cast<PointerType>(
478 BasePtr->getType())->getElementType()->isSized()) {
479 for (unsigned i = 0; i != GEPOperands.size(); ++i)
480 if (!isa<ConstantInt>(GEPOperands[i]))
482 Constant::getNullValue(GEPOperands[i]->getType());
484 getTargetData().getIndexedOffset(BasePtr->getType(),
488 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
498 // This function is used to determin if the indices of two GEP instructions are
499 // equal. V1 and V2 are the indices.
500 static bool IndexOperandsEqual(Value *V1, Value *V2) {
501 if (V1->getType() == V2->getType())
503 if (Constant *C1 = dyn_cast<Constant>(V1))
504 if (Constant *C2 = dyn_cast<Constant>(V2)) {
505 // Sign extend the constants to long types, if necessary
506 if (C1->getType() != Type::Int64Ty)
507 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
508 if (C2->getType() != Type::Int64Ty)
509 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
515 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
516 /// base pointers. This checks to see if the index expressions preclude the
517 /// pointers from aliasing...
518 AliasAnalysis::AliasResult
519 BasicAliasAnalysis::CheckGEPInstructions(
520 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
521 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
522 // We currently can't handle the case when the base pointers have different
523 // primitive types. Since this is uncommon anyway, we are happy being
524 // extremely conservative.
525 if (BasePtr1Ty != BasePtr2Ty)
528 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
530 // Find the (possibly empty) initial sequence of equal values... which are not
531 // necessarily constants.
532 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
533 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
534 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
535 unsigned UnequalOper = 0;
536 while (UnequalOper != MinOperands &&
537 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
538 // Advance through the type as we go...
540 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
541 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
543 // If all operands equal each other, then the derived pointers must
544 // alias each other...
546 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
547 "Ran out of type nesting, but not out of operands?");
552 // If we have seen all constant operands, and run out of indexes on one of the
553 // getelementptrs, check to see if the tail of the leftover one is all zeros.
554 // If so, return mustalias.
555 if (UnequalOper == MinOperands) {
556 if (NumGEP1Ops < NumGEP2Ops) {
557 std::swap(GEP1Ops, GEP2Ops);
558 std::swap(NumGEP1Ops, NumGEP2Ops);
561 bool AllAreZeros = true;
562 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
563 if (!isa<Constant>(GEP1Ops[i]) ||
564 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
568 if (AllAreZeros) return MustAlias;
572 // So now we know that the indexes derived from the base pointers,
573 // which are known to alias, are different. We can still determine a
574 // no-alias result if there are differing constant pairs in the index
575 // chain. For example:
576 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
578 // We have to be careful here about array accesses. In particular, consider:
579 // A[1][0] vs A[0][i]
580 // In this case, we don't *know* that the array will be accessed in bounds:
581 // the index could even be negative. Because of this, we have to
582 // conservatively *give up* and return may alias. We disregard differing
583 // array subscripts that are followed by a variable index without going
586 unsigned SizeMax = std::max(G1S, G2S);
587 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
589 // Scan for the first operand that is constant and unequal in the
590 // two getelementptrs...
591 unsigned FirstConstantOper = UnequalOper;
592 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
593 const Value *G1Oper = GEP1Ops[FirstConstantOper];
594 const Value *G2Oper = GEP2Ops[FirstConstantOper];
596 if (G1Oper != G2Oper) // Found non-equal constant indexes...
597 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
598 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
599 if (G1OC->getType() != G2OC->getType()) {
600 // Sign extend both operands to long.
601 if (G1OC->getType() != Type::Int64Ty)
602 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
603 if (G2OC->getType() != Type::Int64Ty)
604 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
605 GEP1Ops[FirstConstantOper] = G1OC;
606 GEP2Ops[FirstConstantOper] = G2OC;
610 // Handle the "be careful" case above: if this is an array/vector
611 // subscript, scan for a subsequent variable array index.
612 if (isa<SequentialType>(BasePtr1Ty)) {
614 cast<SequentialType>(BasePtr1Ty)->getElementType();
615 bool isBadCase = false;
617 for (unsigned Idx = FirstConstantOper+1;
618 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
619 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
620 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
624 NextTy = cast<SequentialType>(NextTy)->getElementType();
627 if (isBadCase) G1OC = 0;
630 // Make sure they are comparable (ie, not constant expressions), and
631 // make sure the GEP with the smaller leading constant is GEP1.
633 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
635 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
636 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
637 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
638 std::swap(NumGEP1Ops, NumGEP2Ops);
645 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
648 // No shared constant operands, and we ran out of common operands. At this
649 // point, the GEP instructions have run through all of their operands, and we
650 // haven't found evidence that there are any deltas between the GEP's.
651 // However, one GEP may have more operands than the other. If this is the
652 // case, there may still be hope. Check this now.
653 if (FirstConstantOper == MinOperands) {
654 // Make GEP1Ops be the longer one if there is a longer one.
655 if (NumGEP1Ops < NumGEP2Ops) {
656 std::swap(GEP1Ops, GEP2Ops);
657 std::swap(NumGEP1Ops, NumGEP2Ops);
660 // Is there anything to check?
661 if (NumGEP1Ops > MinOperands) {
662 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
663 if (isa<ConstantInt>(GEP1Ops[i]) &&
664 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
665 // Yup, there's a constant in the tail. Set all variables to
666 // constants in the GEP instruction to make it suiteable for
667 // TargetData::getIndexedOffset.
668 for (i = 0; i != MaxOperands; ++i)
669 if (!isa<ConstantInt>(GEP1Ops[i]))
670 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
671 // Okay, now get the offset. This is the relative offset for the full
673 const TargetData &TD = getTargetData();
674 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
677 // Now check without any constants at the end.
678 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
681 // If the tail provided a bit enough offset, return noalias!
682 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
687 // Couldn't find anything useful.
691 // If there are non-equal constants arguments, then we can figure
692 // out a minimum known delta between the two index expressions... at
693 // this point we know that the first constant index of GEP1 is less
694 // than the first constant index of GEP2.
696 // Advance BasePtr[12]Ty over this first differing constant operand.
697 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
698 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
699 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
700 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
702 // We are going to be using TargetData::getIndexedOffset to determine the
703 // offset that each of the GEP's is reaching. To do this, we have to convert
704 // all variable references to constant references. To do this, we convert the
705 // initial sequence of array subscripts into constant zeros to start with.
706 const Type *ZeroIdxTy = GEPPointerTy;
707 for (unsigned i = 0; i != FirstConstantOper; ++i) {
708 if (!isa<StructType>(ZeroIdxTy))
709 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
711 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
712 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
715 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
717 // Loop over the rest of the operands...
718 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
719 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
720 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
721 // If they are equal, use a zero index...
722 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
723 if (!isa<ConstantInt>(Op1))
724 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
725 // Otherwise, just keep the constants we have.
728 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
729 // If this is an array index, make sure the array element is in range.
730 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
731 if (Op1C->getZExtValue() >= AT->getNumElements())
732 return MayAlias; // Be conservative with out-of-range accesses
733 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
734 if (Op1C->getZExtValue() >= VT->getNumElements())
735 return MayAlias; // Be conservative with out-of-range accesses
739 // GEP1 is known to produce a value less than GEP2. To be
740 // conservatively correct, we must assume the largest possible
741 // constant is used in this position. This cannot be the initial
742 // index to the GEP instructions (because we know we have at least one
743 // element before this one with the different constant arguments), so
744 // we know that the current index must be into either a struct or
745 // array. Because we know it's not constant, this cannot be a
746 // structure index. Because of this, we can calculate the maximum
749 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
750 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
751 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
752 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
757 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
758 // If this is an array index, make sure the array element is in range.
759 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
760 if (Op2C->getZExtValue() >= AT->getNumElements())
761 return MayAlias; // Be conservative with out-of-range accesses
762 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
763 if (Op2C->getZExtValue() >= VT->getNumElements())
764 return MayAlias; // Be conservative with out-of-range accesses
766 } else { // Conservatively assume the minimum value for this index
767 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
772 if (BasePtr1Ty && Op1) {
773 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
774 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
779 if (BasePtr2Ty && Op2) {
780 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
781 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
787 if (GEPPointerTy->getElementType()->isSized()) {
789 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
791 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
792 assert(Offset1 != Offset2 &&
793 "There is at least one different constant here!");
795 // Make sure we compare the absolute difference.
796 if (Offset1 > Offset2)
797 std::swap(Offset1, Offset2);
799 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
800 //cerr << "Determined that these two GEP's don't alias ["
801 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
808 // Make sure that anything that uses AliasAnalysis pulls in this file...
809 DEFINING_FILE_FOR(BasicAliasAnalysis)